Process and apparatus for conversion of hydrocarbons



Dec. 30, 1958 J. w. BEGLEY E TAL 2,866,836

PROCESS AND APPARATUS FOR CONVERSION OF HYDROCARBONS Filed Oct, 22, 1954 2 Sheets-Sheet 1 PINCH SECTION I0 LENGTH OF FURNACE CRACKING SECTION FT.

/l (l l] ATTORNEYS 'J. W. BEGLEY ETAL Dec. 3o, 195s PROCESS AND APPARATUS FOR CONVERSION OF HYDROCARBONS Filed 001'.. 22, 1954 2 Sheets-Sheet 2 FUDDOma J.W. BEGLEY S m m w. m

R.R.GOINS mm Q Nm wm A I I'l JmDu Q Dumm M.

A7' TORNEYS United tes atent PROCESS AND APPARATUS FOR 'CONVERSION F HYDROCARBONS John W. Bagley and Robert RrGoins, Bartlesville, Okla.,

assignors to Phillips Petroleum Company, a corporation of Delaware Application October 22, 1954, Serial No. 463,918

8 Claims.` (Cl. Mtl- 683) cracking of low boiling hydrocarbons received comparatively little attention. Because of apparatus limitations imposed by the high reaction temperatures involved and the lack of understanding of the bestmanner of operation, early developments excluded the cracking of low boiling hydrocarbons. Still another deterrent in the development of successful processes was the availability of vast supplies of-heavy naphthas which could be cracked by more easily manageable' processes to form easilyl puriable products in high yield. Recent advancements made in organic chemistry have resulted in such an increased demand for petro-chernical starting materials, such as acetylene and ethylene, that it is no longer possible to rely on the old sources of supply for these materials. The demand for ethylene has reached such proportions that it cannot be supplied from refinery streams without upsetting the balance in the production of motor and aviation fuels. Furthermore, commercial production of acetylene by reacting calcium carbide with water is too expensive and is limited to amounts far too low to satisfy the demand for acetylene as a chemical synthesis starting material. Accordingly, the development of successful processes for producing unsaturated hydrocarbons by the cracking of low boiling hydrocarbons has in recent years taken on added importance.

Various methods for the pyrolysis of gaseous hydrocarbons'have been proposed which involve the use of a variety of heat sources, including externally heated tubes, electrically heated resistance elements, and spark'or electrical discharges. The lack of cheap electric power has `also drawn attention to other possible methods of'heating, such as by the combustion of preheated natural gas with preheated compressed air. In such latter processes when utilizing regenerative furnaces, av stream o f air and fuel gas is burned in, or hot combustion products passed through, a refractory checkerwork so as to heat it to a high temperature. After the hot gases have heated the checkerwork tothe desired temperature, the flow of combustionv gases-is terminated, and thereafter the reactant materials tobe treated are passed through the'heated checkerwork in order to bring the materials to reaction temperature. v

In a particularly useful regenerative furnace of this type,v utilized for the thermal cracking of hydrocarbons, suchas methane, etliane, propane or butane, to produce unsaturated hydrocarbons, such as ethylene or acetylene, ab, elongated checkerwork of refractory material is pro- Ffice vided at either end of a central combustion chamber. Air is passed in one direction through one of the checkerwork structures while a fuel gas is introduced into the central combustion chamber. The fuel gas and air burn in the combustion chamber, and thereafter the resulting combustion gases flow through one of the refractory checkerworks. When this checkerwork has reached the desired temperature, the flow of air and fuel is terminated, and the materials to be cracked or otherwise converted are passed in the opposite direction through the heated refractory where the desired cracking or other reaction occurs. l

After a timed reaction period, the flow of reactant materials is stopped,` and air is passed through the furnace in a direction opposite to that of its first introduction. At the same time, fuel gas is introduced into the central combustion chamber to mix with the air and form a combustible mixture which is burned therein to form hot combustion gases to heat the refractory checkerwork downstream of the combustion chamber. When the checkerwork attains the desired temperature, the materials to be converted are passed through the heated refractory.

We have now discovered that when utilizing a regenerative furnace of the type described above, having similar refractory cracking sections, a very close'temperature approach exists in the center of the cracking sections. The portion of-the cracking sections in which the temperature of thegases, i. e., the combustion gases or thel reaction products, and the refractory material, are substantially equal may be termed the pinch section and denotes that portiony of the cracking section where substantially no net heat transfer occurs between the gases andthe refractories. Ina regenerative furnace, it is desirable that the length of the pinch section be as short as possible in order'to reduce the over-all length of the furnace. Figure 1 of the drawing illustrates graphically the temperature conditions existing in a cracking section of a regenerative furnace of the type described. Curves 1 and 2 represent, respectively, the temperature of the combustion gases and the temperature of the hydrocarbon reactant material as these gases pass through the refractory checkerwork. The combustion gases-enter the checkerwork at a higher temperature and leave at a lower temperature while the hydrocarbons are introduced at a lower temperature and pass therefrom at'a higher temperature. That portion of the curves in which the gases undergo substantially no change in-temperature is labeled pinch section and designates that part of the furnace in which there is substantially no net transfer of heat between the gases and the refractory. lt is noted that a major portion of the furnace is occupied by the pinch'secton. lnorder to decrease the length of the furnace, it is desirable to maintain the pinch section as short as possible, and in accordance with this invention, means are provided for attaining this result.

A regenerative furnace of the type described, having a single combustion chamber disposed between a pair of refractory checkerworks, cannot be used satisfactorily to crack the heavier hydrocarbons because of the forniation of carbonaceous materials within the cracking sections. In order to operate such a furnace `on a liquid hydrocarbon feed, it becomes necessary to preheat the feed and then inject same into the furnace in vaporized form. It would be desirable if the feedcould be introduced directly into the furnace without prior heating, and the necessary preheating and vaporization of the'liquid feed effected within the furnace itself. ln accordance with the present invention, a regenerative furnace is provided in which this desirable result is attained.

The following are objects of this invention. n. It is an object of the invention rto provide an improved regenerative furnace for use in the conversion of hydrocarbons.

Another object of the invention is to provide improved methods for` the thermal conversion of hydrocarbons. Still another object of the invention is `to decrease `the length ofthe regenerative furnace by reducing the pinch section `of the furnace. f y

A further object of theinvention is to provide a novel regenerative furnace which is especiallysuitable for the cracking of hydrocarbons which are normally liquid.l

Still further objects` and advantages of the invention will `become apparent to one skilled in the art upon con` sideration of the following disclosure.

Broadly speaking, the present invention resides' in a novel regenerative furnace and the use of the furnace in the conversion 1of hydrocarbons. -The regenerative furnacecomprises a `series of three refractory checkerworks separated bymixing zones, each formed in the shape of a venturi. In the operation of the furnace, air introduced into one end thereof passes through a refractory checkerwork where it is heated. t The heated air thereafter enters one of the mixing zones where it is thoroughly mixed with a fuel gas,` forming a combustible mixture which burns therein. The resulting combustion products then ow through the furnace heating the other two refractory checkerworks.` At lthe end of the regeneration cycle, steam is introduced into the opposite end of the furnace passing through the other end checkerwork, Ithereby heating the steam. The preheated steam thereafter enters the other of the mixing zones and is mixed therein with the hydrocarbon feed. The feed is thereby raised to a temperature approaching the desired cracking ,t temperature, and the resulting mixture then i and oxidant are burned. The mixing chambers are lined with refractory material 27 so placed as to form a chamber in the form of a venturi comprising a converging section 28, a throat section 29 and a diverging section 31. As indicated in Figure 6, the mixing sections have a circular cross-section. It should be apparent that as a result of joining the mixing sections with the refractory masses, which have a rectangular cross-section, the resulting pattern of openings through the refractory masses is likewise circular as shown in Figure 5. Communicating with the mixing chambers 24 and 26 are uid introduction means 32 and 33 provided, respectively, with d I ow control means 34 and 36. While each of the mixing chambers is shown as having two uid introduction enters the `center refractory checkerwork where it is i cracked, thetcracked gases thereafter owing into the end checkerwork for rapid quenching to a temperature at which they` arestable. By mixing the hydrocarbon feed with preheated steam so as to raise the temperature of the feed to near the desired cracking temperature prior to introduction of the feed into the cracking `section of thefurnace, it is posible to substantially reduce the pinch section found in conventional regenerative furnaces.

A more complete understanding of the invention may be obtained by reference to the following description and the drawing, in which:

Figure 1 is a graph illustrating the pinch section" existing in a conventional regenerative furnace;

Figure 2 is anelevation, partially in section, of a regenerative furnace in accordance with this invention;

Figure 3 `is a plan view of a refractory tile suitable for use. in the regenerative furnace of this invention;

Figure,4 is an end view of the refractory tile of Figure 3; u

Figure 5 is a cross-sectional view taken along line 5,-5 of Figure 2; and d t d Figure 6 is a cross-sectional view taken along line 6-6 of, Figure 2. d ,t

Referring now to thedrawing and linparticular to Figure 2, a regenerative furnace `10 is illustrated which comprises a shell `11 lined `with two layers 12 and 13 of insulating material. The inner layer 13 of insulating material isformed of a more refractory material than outer layer 12. Disposed withininsulated shell 11 there are `three spaced-apart,` similar refractory masses 14, 16 and 17 which constitute the heat exchangers of the furnace. These refractory masses are built up of refractory tiles similar to tile 18 shown in Figures and 4.

means, it is to be understood that additional means may be provided without departing from the scope of the invention.

Plenum chambers 37 and 38, connected to either end of the regenerative furnace, provide means for introducing reactant materials into the furnace. Each of the plenum chambers may be provided with a perforated distributor plate 39 to facilitate even distribution of the reactant material across and through the cross-sectional area of the refractory masses.

Conduit 41, through which an oxidant is introduced, is connected by a three-way valve 42 to a conduit 43. Conduit 43 in turn is connected through a three-way valve 44 to a conduit 46 which communicates with plenum chamber 37 or, alternatively, to a conduit 47 which communicates with plenum chamber 38. Valve 42 is also adapted to attach steam conduit 48 to conduit 43 and, thence, to conduits 46 and 47, as determined by the setting of valve 44. Conduits 46 and 47 are also selectively connected by a three-way valve 50 to an eluent conduit 49 which leads to a product recovery system 51, or other disposal, as desired. Timer 52 is operatively connected to ow control means 34 and 36 and to three-way valves 42, 44 and 50, thereby providing means for sequentially changing the cycles of operation of the regenerative furnace. A timer suitable for controlling the cycles of operation is manufactured by Formed in the upperand lower surfaceselQtand `21 of V functions as a `coinbustionchamber wherein a fuel gas Taylor Instrument Companies, Rochester, New York.

The regenerative furnaces of this invention are especially adapted for carrying out processes for the production of `unsaturated hydrocarbons, -such as acetylene, ethylene, and mixtures of acetylene and ethylene. The reaction temperatures for such processes will vary in the approximate range of 1250 F. to 2700" F. More specifically, in the acetylene process, the reaction temperature is preferably maintained between about 2200 F. and 2700 F., in the process for the production of acetylene, and ethylene, between about 1700" F. and 2200 F., and in the ethylene process, between about 1250 F. and 1700"` F. The reaction times for the several processes are in the following approximate ranges: for acetylene, betwee 0.0001 and 0.2 seconds; for a mixture of acetylene and ethylene, between 0.01 and 0.2 second; and for ehtylene, between 0.01 and 2 seconds. From this consideration of reaction temperatures and reaction times, it is apparent that the reaction ltimes vary inversely with the reaction temperatures, i. e., the higher the reaction temperature, the shorter the reaction time.

`A wide variety of hydrocarbon feedstocks can be used in the practice of the processes of this invention. Those which can be suitably used include methane, ethane, propane, butane and mixtures of these hydrocarbons and/or their corresponding olefins. The regenerative furnace of this invention is also particularly well adapted for use in processes for the cracking of hydrocarbons `which are normally liquid. While it is within `the scope of the invention to preheat the liquid hydrocarbon feed prior to introduction into the furnace, it is a feature of this invention that the liquid hydrocarbon feed may be` introduced directly into the furnace without precracking or preheating.

5. Oxidants which' can. berused inpthe process `of this invention includev oxygen, air, and'oxygen-enriched air'. Any `suitable fuel,` preferably, a clean burning fuel, can be utilized iii the practice'of this invention. Gaseous or liquid hydrocarbons are preferably usedas fuels, and process olf-gases from the process of this invention or other processes can be advantageously employed. When using` a liquid hydrocarbon, the fuel isV introduced into the furnace in vaporized form.

In the operation of the .regenerative furnace of Figure y2, during the regeneration cycle, valves 42 and 44 are in such a position that an oxidant, such'as air, is forced by a blower (not shown) through conduits 41, 43 and 47 into plenum chamber 38, from which it passes into passageways 23 of refractory mass 17. Plenum chamber 38 and distributor plate 439 disposed therein provide for even distribution of .air across the face of refractory mass-17 and assures even'ow of the air therethrough. It is assumed .that.the furnace has been lpreviously broughtl tooperating temperature during a start-up cycle in which fuel and air passed into the furnace are ignited by a suitable ignition means, e. g., a burning torch introduced into the combustion chamber. The resulting combustion productsV are then passed through the furnace until it is preheated. to the desired temperature.

The air in passing through refractory mass 17 is heated to a temperature at least as high as the ignition temperature of the fuel gas introduced into mixing chamber. 26 through uid introduction means 33. The fuel gas may be preheated prior to injection into the mixing chamber. By providing a mixing chamber in the form of a venturi, a very thorough and efficient mixing of the fuel gas is obtained as a result of the extremely turbulent condition set up within the chamber upon impingement of the fuel and air.l The combustible mixture of the air andfuel gas within mixing chamber 26 burns therein forming combustion products, thetemperature of which depends upon the amount of air and the amount of fuel introduced into the chamber. The combustion products thereafter ow through passageways 23 o-f refractory mass 16, mixing chamber 24 and passageways 23 of refractory mass 14, heating the refractories of these masses tothe desired cracking temperature. The combustion products then pass into plenum chamber 37, and thence, through conduits 46 and 49 into product recovery system 51 where they may be used for heating or other purposes.

At the conclusion of a predetermined length of time as determined by the setting of timer 52, valve 42 is r actuated by timer 52 to tansfer conduit 43 from its connection with conduit 41 to a connection with conduit 48. The timer also operates to close flow control means 36 contained in fuel introduction means 33, to open flow control means 34 contained in feed introduction means 32 and to reverse the settings of valves 44 and 50 so that conduit 43 is connected to conduit 46 and conduit 47 is connected to conduit 49. An interval of one minute is a suitable reaction period and regeneration period for the cracking of propane to form acetylene. In general, the time interval will depend upon the specific process being carried out and the particular hydrocarbon feed being converted. As a result of the movement of valves 42 and 44, the process cycle .-commences, and steam now passes through conduits 48, 43 and 46 into plenum chamber 37. As previously noted, the combination of the plenum chamber and distributor plate 30 provides for even flow through refractory mass 14. On contacting hot refractory mass 14, the steam is heated to a temperature approaching that of the desired cracking temperature. The preheated steam thereafter enters mixing chamber 24 wherein it is thoroughly mixed withthe hydrocarbon feed introduced into this chamber through Huid intro-duction means 32, thereby ,raising the temperature of the feed to near the desired cracking temperature.' When .utilizing ai liquid hydrocarbon feed, the feed is vaporized vand preheated asf-a result of being mixed with .the preheated steam. The

mixture of steam andhydocarbon feed then enters pas-f sageways 23 of refractory mass 16 wherein it undergoes the desired cra-cking reaction. The reaction products thereafter pass into mixing chamber 26 and then enter passageways 23 `ofrefractory mass 17,' which has been previously cooled by passage of air therethrough, for rapid quenching to a temperature at which the products are stable, e. g., a temperature inthe range of about 400- F.

to 1000 F. A'fte'r being quenched in. refractory mass into the lfurnace thro-ugh conduit 47 to start the regen-1 eration cycle which continues as previously described. Theprocess .cycle is recommenced by timer 52 operating to close ow control means 36, to open ow control means 34y and to reverse the settings of three-way valves 42,' 44 and 50. The process cycle is now carried out by introducting steamwinto the furnace through conduit 46 for heating within refractory mass 14, the resulting preheated steam .thereafter being mixed with hydrocarbon feed in mixing chamber 24 prior to cracking in refractory mass 16 and quenching of the resulting reaction prod-1 ucts in refractory mass 17. Thereafter, the regeneration and process cycles are repeated at thepredetermined time interval to produce the desired product.

A more comprehensive vunderstanding of the inven-z tion maybeobtainedby referring to the following illustrativeexamples which are not intended, however, to be unduly limitative of the invention.

Example l A regenerative furnace of a conventional type described herein as having similar cracking sections separated by a central combustion chamber is utilized to convert ethane. The hydrocarbon feed rate is 72,450 pounds of ethane per day, the combustion temperature is about 2840" F., and the exit combustion gas temperature is about l000 F. The pressure drop across the cracking sections during the combustion cycle is 1.85 p. s. i. in order to convert ninety-five per cent of the ethane, refractory cracking sections each having a length of 14.4 feet and a 27x90 inch cross section are required. The yield of ethylene is 63.5 pounds per pounds of ethane cracked.

Example II A regenerative furnace similar to the one illustrated in Figure 2 is utilized to convert ethane. The hydrocarbon feed rate is 91,300 pounds of ethane per day, and steam is charged at the rate of 210,000 pounds per day. The combustion temperature is about 2840 Fl while the exit combustion gas temperature is about 1000 F. The pressure drop across the cracking section during the combustion cycle is 1.85 p. s. i. In order to convert ninety-five percent of the ethane, a refractory cracking section having a length of 6.4 feet and a 27x90 inch cross section is required. The yield of ethylene is 76.0 pounds per 100 pounds of ethane cracked. From a consideration of Examples I and II, it is apparent that the pinch section found in conventional regenerative furnaces is substantially reduced in the furnace of this invention. Furthermore, it is noted that a higher product yield `is obtainable when carrying out the cracking reaction in thevv furnace of this invention.

Several advantages accrue from utilizing the regenerative furnace of this invention in processes for the conversion of hydrocarbons. By heating the steam and then mixing the preheated steam with the hydrocarbon feed so as to raise the temperature of the feed to near that of the cracking reaction, it is possible to reduce the pinch section formed in the cracking sections of conventional regenerative furnaces.` By reducing the pinch section as a result of transferring heat to the cracking section in the preheated steam,the over-all length of the furnace is shorter than that of conventional furnaces. Witha shorter furnace, a higher fiow rate of hydrocarbon feed can be used with the same pressure drop as is encountered in the caseuwhere the flow rate is lower and `the furnace longer. Furthermore, by utilization of preheated steam, as in this invention, formation of carbonaceous materials within the furnace is substantially eliminated. This latter aspect of the in vention` is especially applicable to the cracking of the heavier hydrocarbons which generally results in an appreciable formation of such materials. Accordingly, the regenerative furnace of this invention can be very advantageously used in the cracking of hydrocarbons which are normally liquid although it is to be understood that the furnace can be used equally as well in the cracking of light hydrocarbons. The use of a steam diluent is also especially advantageous when producing acetylene, it having been found that a higher product `yield can be attained when using steam in this process. Additional advantages arise from the use of the mixing chambers disposed between the refractory masses of the furnace. As a result of employing the mixing chambers, a more efiicient and thorough mixing of the reactant materials is obtained, thereby giving more efficient combustion and cracking reactions. Furthermore, the mixing chambers serve to redistribute the gases so that an even and uniform gas ow is obtained through the refractory masses. As a result, the refractory masses are uniformly heated so that overcracking and undercracking of the hydrocarbon feed are prevented. Because of the elimination of overand undercracking, `secondary reactions which tend to form tar and coke are reduced to a minimum and a higher produce yield is made possible.

As will be evident to those skilled in the art, various modifications of this invention can be made or followed without departing from the spirit or the scope of the disclosure.

We claim:

1. A regenerative furnace which comprises, in combination, first, second and third refractory checkerworks arranged in longitudinal alignment; longitudinal passageways extending through said refractory checkerworks; a first mixing chamber formed of refractory material in the shape of a venturi, said chamber being positioned between said first and second refractory checkerworks; lateral fluid introduction means communicating with said first fixing chamber, said lateral introduction means communicating at its other end with a source of fiuid to be endothermically converted; a second mixing chamber formed of refractory material in the shape of a venturi, said chamber being positioned between said second and third refractory checkerworks; lateral fluid introduction means communicating with said second mixing chamber; means for `introducing steam into said first refractory checkerworks; and means for introducing oxidant into said third refractory checkerwork.

2. A regenerative furnace which comprises, in combination, an elongated, closed shell; a first refractory checkerwork disposed in one end of said shell; a second refractory checkerwork disposed in an intermediate portion of said shell; a third refractory checkerwork disposed in the other end of said shell; longitudinal passageways extending through each said refractory checkerworks; a first mixing chamber formed of refractory material in the shape ofa venturi, said chamber being positioned bewteeu said first and Second Arefractory 4checkerworks; lateral fluid introduction means communicating with said first mixing chamber, said lateral introduction means communicating at its other end with a source of fluid to be endothermically converted; a second mixing chamber formed of refractory material in the shape of a venturi, said cham` ber being positioned between said second and third refractory checkerworks; lateral fiuid introduction means communicating with said second mixing chamber; means for introducing steam into one end of said shell; and means for introducing oxidant into the other end of said shell.

3. The regenerative furnace of claim 2 in which said first and second mixing chambers each comprise a converging section, a throat section and a diverging section and said uid introduction means communicate with said throat sections of said mixing chambers.

4. The regenerative furnace of claim 2 in which said steam introduction means comprises a plenum chamber having a conduit attached thereto, connected to one end of said shell and said oxidant introduction means comprises a plenum chamber having a conduit attached thereto connected to the other end of said shell.

S. A process for converting hydrocarbons which comprises passing steam into a first refractory checkerwork; heating Said steam within said first refractory checkerwork to a desired temperature; passing heated-steam from said first refractory checkerwork directly into a mixing chamber; introducing liquid hydrocarbon feed into said mixing chamber and admixing said feed with said steam therein; passing the resulting mixture of heated steam and hydrocarbon feed into a second refractory checkerwork; cracking said hydrocarbon feed within said second refractory checkerwork; passing the resulting reaction products into a third refractory checkerwork; quenching said reaction products within said third refractory checkerwork; and removing said cooled reaction products from said third refractory checkerwork; then terminating the flow of said hydrocarbon and said steam.

6. A process for converting hydrocarbons which comprises passing air through a first refractory checkerwork into a first mixing chamber; introducing fuel gas laterally into said first mixing chamber so as to form a combustible mixture; burning said combustible mixture within said first mixing chamber; passing the resulting combustion gases through second and third refractory checkerworks in order to heat same to a desired temperature; terminating the supply of air and fuel gas; introducting steam into said third refractory checkerwork in order to superheat said steam; passing the resulting superheated steam into a second mixing chamber; introducing hydrocarbon feed laterally into said second mixing chamber and therein forming a mixture of steam and hydrocarbon feed; passing said mixture of steam and hydrocarbon feed into said second refractory checkerwork; cracking said hydrocarbon feed within said second refractory checkerwork; passing the resulting reaction products from said second refractory checkerwork through said first mixing chamber and into said first refractory checkerwork; cooling said reaction products within said first refractory checkerwork to a temperature at which they are comparatively stable; and removing said cooled reaction products from said first refractory checkerwork.

7. The process of claim 6 in which a liquid hydrocarbon feed is introduced into said second mixing chamber and said feed is vaporized and heated therein to a temperature approaching the desired cracking temperature by mixing with said preheated steam.

8. A process for converting hydrocarbons which comprises the following steps: passing air through a first refractory checkerwork into a first mixing chamber; introducing fuel gas laterally into said first mixing chamber soas to form a combustible mixture; burning said combustible mixture within said first mixing chamber; passing the resulting combustion gases through second and third refractory checkerworks in order to heat same to a desired temperature; terminating the supply of air and fuel gas; introducing steam into said third refractory checkerwork in order to superheat said steam; passing the resulting superheated steam into a second mixing chamber; introducing hydrocarbon feed laterally into said second mixing chamber and forming a mixture of steam and hydrocarbon feed; passing said mixture of steam and hydrocarbon feed into said second refractory checkerwork; cracking said hydrocarbon feed within said second refractory checkerwork; passing the resulting reaction products from said second refractory checkerwork through said rst mixing chamber and into said first refractory checkerwork; cooling said reaction products within Said first refractory checkerwork to a temperature at which they are comparatively stable; and removing said cooled reaction products from said irst refractory checkerwork; terminating the supply of said hydrocarbon feed and said steam; and then repeating the said steps 10 herein before recited, thus always passing the said hydrocarbon feed gases in the same direction through the checkerworks during the cracking step and always passing the combustion gases through the checkerworks in the same direction opposite to the direction during the cracking step.

References Cited in the le of this patent UNITED STATES PATENTS 2,046,502 Cooke July 7, 1936 2,393,333 Milbourne Jan. 22, 1946 2,622,864 Hasche Dec. 23, 1952 2,630,461 Sachsse et al Mar. 3, 1953 2,645,673 Hasche July 14, 1953 2,666,734 Findlay Jan. 19, 1954 2,692,819 Hasche et al Oct. 26, 1954 FOREIGN PATENTS 583,851 Germany Sept. 13, 1933 (Addition to No. 578,311, June 12, 1933) 

1. A REGENERATIVE FURNACE WHICH COMPRISES, IN COMBINATION, FIRST, SECOND AND THIRD REFRACTORY CHECKERWORKS ARRANGED IN LONGITUDINAL ALIGNMENT; LONGITUDINAL PASSAGEWAYS EXTENDING THROUGH SAID REFRACTORY CHECKERWORKS; A FIRST MIXING CHAMBER FORMED OF REFRACTORY MATERIAL IN THE SHAPE OF A VENTURI, SAID CHAMBER BEING POSITIONED BETWEEN SAID FIRST AND SECOND REFRACTORY CHECKERWORKS; LATERAL FLUID INTRODUCTION MEANS COMMUNICATING WITH SAID FIRST FIXING CHAMBER, SAID LATERAL INTRODUCTION MEANS COMMUNICATING AT ITS OTHER END WITH A SOURCE OF FLUID TO BE ENDOTHERMICALLY CONVERTED; A SECOND MIXING CHAMBER FORMED OF REFRACTORY MATERIAL IN THE SHAPE OF A VENTURI, SAID CHAMBER BEING POSITIONED BETWEEN SAID SECOND AND THIRD REFRACTORY CHECKERWORKS; LATERAL FLUID INTRODUCTION MEANS COMMUNICATING WITH SAID SECOND MIXING CHAMBER; MEANS FOR INTRODUCING STEAM INTO SAID FIRST REFRACTORY CHECKERWORKS; AND MEANS FOR INTRODUCING OXIDANT INTO SAID THIRD REFRACTORY CHECKERWORK.
 5. A PROCESS FOR CONVERTING HYDROCARBONS WHICH COMPRISES PASSING STEAM INTO A FIRST REFRACTORY CHECKERWORK; HEATING SAID STEAM WITHIN SAID FIRST REFRACTORY CHECKERWORK TO A DESIRED TEMPERATURE; PASSING HEATED-STEAM FROM SAID FIRST REFRACTORY CHECKERWORK DIRECTLY INTO A MIXING CHAMBER; INTRODUCING LIQUID HYDROCARBON FEED INTO SAID MIXING CHAMBER AND ADMIXING SAID FEED WITH SAID STEAM THEREIN; PASSING THE RESULTING MIXTURE OF HEATED STEAM AND HYDROCARBON FEED INTO A SECOND REFRACTORY CHECKERWORK; CRACKING SAID HYDROCARBON FEED WITHIN SAID SECOND REFRACTORY CHECKERWORK; PASSING THE RESULTING REACTION PRODUCTS INTO A THIRD REFRACTORY CHECKERWORK; QUENCHING SAID REACTION PRODUCTS WITHIN SAID THIRD REFRACTORY CHECKERWORK; AND REMOVING SAID COOLED REACTION PRODUCTS FROM SAID THIRD REFRACTORY CHECKERWORK; THEN TERMINATING THE FLOW OF SAID HYDROCARBON AND SAID STEAM. 